The present invention relates to a miniaturized universal electromagnet capable of operation in wide voltage range. After it is energized, its moving core can move in one direction. After the electromagnet is deenergized, potential energy of the moving core (i.e., gravity, spring force or elastic deformation during the movement of the moving core after the electromagnet is energized returns the moving core to its initial position. The electromagnet is particularly applicable as an electromagnet for applications requiring traction, braking, vibration, electromagnetic valve and contactor operations.
A conventional electromagnet, whether A.C. or D.C., consists of a static core, a moving core, a coil package, a demagnetizing shim or gap and an electric control component. Due to many limiting factors the magnitude of working magnetic flux-density of an electromagnet is generally restricted to a low range usually 7 kilogauss or less than 7 kilogauss. The requirements for working duty and coil temperature rise require a large amount of coil copper, a low utilization coefficient of copper and iron materials, a low weight economy index (work done by electromagnet/weight of electromagnet, unit: m.sup.2 /s.sup.2), short mechanical life and low working reliability. Taking the MZD.sub.1 -200 brake electromagnet as an example, its weight is about 16 kg, its mechanical life is below 600 thousands operating cycles. Further, a conventional D.C. brake electromagnet of the same capacity is even heavier.
A short stroke direct acting D.C. brake electromagnet with U-shaped construction is known. When the core of this type of electromagnet is made of low carbon steel with a weight about 5.5 kg, its working magnetic flux-density reaches 10-12 kilogauss for the same capacity as MZD.sub.1 -200. When its core is made of electric steel material having high magnetic flux-density, its working magnetic flux-density reaches 15-16 kilogauss.
A shift-switching control circuit having an A.C. source, a current-limiting capacitor and bridge rectifier has been adopted for the electromagnet (see FIG. 1). One terminal of the shift-switch SW is connected to one pole of operating source Uac, the other terminal to an A.C. side of the bridge rectifier Z. A current-liminting capacitor link X is connected in parallel with switch SW. Circuit X consists of a capacitor C.sub.1, a resistor R.sub.1 and a resistor R.sub.2, R.sub.1 being in parallel with C.sub.1, and in series with R.sub.2. The other A.C. side of Z is connected to the other pole of the source Uac. The coil W is connected to the D.C. sides of Z. If quick releasing of the electromagnet after deenergization is required, a quick release contact FK, whose on-off operation is synchronized with the operating source, may be added in one terminal of W. The contact FK is in series with W. The two terminals (nodes a and b in FIG. 1) of FK are connected to a resistor R.sub.3. When the electromagnet is energized and its closing movement starts, the contact at SW is in an "on" state and enables the full voltage to be applied onto the coil W through bridge rectifier Z. SW breaks just before the electromagnet accomplishes the closing movement, and then circuit X is put into a working state thus reducing the working voltage of coil W to a small fraction of that in the starting state while still being sufficient to sustain holding. In all existing designs, the lower limit of the closing voltage is taken and adjusted according to the value corresponding to about 0.80 of the rated voltage of the electromagnet in a hot state. Further, according to existing techniques, the starting current-density in the coil cannot significantly exceed 25 A/mm.sup.2.
The lower limit of the closing voltage of the conventional electromagnet is generally over 0.80-0.85 of the rated voltage. If this lower limit is exceeded, damaging effects to performance and service life of the electromagnet and the coil will result.
In conventional D.C. electromagnets, the attraction-counteraction matching characteristic is generally considered theoretically better and easier to affect an optimized matching. In fact, this is not the case. In practice, under the same condition of main contact systems, the mechanical life of a D.C. electromagnet is obviously lower than that of an A.C. one in both domestic as well as oversea products. For example, the mechanical life of a new series of D.C. contactor is only one half of that of a new series of A.C. contactor of the same capacity. When a contactor is closing, a lot of kinetic energy is released in the form of impact of the cores. This impact energy increases rapidly as a function of contactor capacity. As a result, the mechanical life of a large-capacity device is only one half or even less than that of a small capacity one. Thus, any direct-acting type contactor over 60 A has a rigid and ventilated metal seat to contain the electromagnet which is fitted in the seat through buffered coupling parts. The mounting holes of contactor can only be located on the seat.
A conventional T-shaped electromagnet (not used for small-capacity devices) usually has only one contact surface for closing on the T-shaped moving core, in order to reduce detrimental closing impact. Due to the inherent attracting characteristic of the T-shaped electro-magnet, no contactor over 40 A is used with the T-shaped solenoidal electromagnet.
Some of the existing A.C. electromagnets may have their static energy saving rate over 96% when energy saving and noiseless running measure are implemented. However, static power consumption of a D.C. traction electromagnet or brake electromagnet consuming static power, equally effective reduction measures are not available. Large and medium conventional capacity brake electromagnets (used in driving brakes of braking torque over 60 kg.m) are now obsolete and substituted by hydraulic products because of their unadaptability for mass production. However, electromagnetic-hydraulic or electrohydraulic brakes are not likely to be used extensively owing to their complex structures, high cost, etc.